International System of Units

• https://en.wikipedia.org/wiki/International_System_of_Units

US

• Is there a single historic event which could be changed to cause the USA to use SI units?

Stop one ship from either sailing into a storm or (later) being taken over by pirates.

In 1793, Thomas Jefferson ordered a set of instruments from France that would let the US calibrate to SI units, but the ship hit a storm at sea, blowing his ship into the Caribbean. There it was attacked by pirates (British privateers). The materials never arrived. By the time France sent a second set, US had a new Secretary of State who didn’t like metric system.

You either need to delay the ship departure (so it misses the storm) or help take down the pirates. Minimal intervention.

• Pirates — yes, pirates — may be why the U.S. doesn’t use the metric system
• How Pirates Of The Caribbean Hijacked America’s Metric System